Golf ball

ABSTRACT

A golf ball is provided that has a hard sphere core or layer that exhibits a controlled vibrational response. The vibrational response may be controlled by tailoring the stiffness or damping of the sphere with at least one element, such as a groove(s) or any other type of indentation in the hard sphere core. The groove (or grooves) serves to locally reduce the wall thickness of the hollow metal sphere core, thereby reducing the stiffness of the core by allowing larger deformations under a load without significantly reducing the total mass of the core. This results in a golf ball that is legal for play and capable of drive distances essentially equivalent to those of currently available high performance golf balls, but that also maintains a high moment of inertia, allowing less hooks and slices during play.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation in part of U.S. patentapplication Ser. No. 10/756,185, filed Jan. 13, 2004, which is acontinuation of U.S. Pat. No. 6,705,957, issued Mar. 16, 2004, which isa continuation of U.S. Pat. No. 6,004,225, issued Dec. 21, 1999, whichclaims priority to U.S. Provisional Patent Application No. 60/036,196,filed Jan. 16, 1997, each of which are hereby incorporated by referencethereto.

FIELD OF THE INVENTION

The present invention relates generally to an improved multi-piece golfball, and more particularly, a multi-piece golf ball including a hardspherical core or layer with improved characteristics.

BACKGROUND OF THE INVENTION

In order to meet United States Golf Association (“U.S.G.A.”)specifications, a golf ball must meet certain test criteria relating toweight, size, initial velocity, overall distance (carry and roll), andspherical symmetry. In general, a golf ball must not weigh more than1.620 ounces avoirdupois, must have a diameter of not less than 1.680inches, must have a maximum initial ball velocity of 250 feet per second(plus a maximum 2% tolerance) as measured on a standard U.S.G.A. balltesting machine, must not have an overall distance that exceeds 317yards (plus a maximum 3 yard tolerance) as measured by the U.S.G.A.overall distance test procedure, and must not be designed, manufacturedor intentionally modified to have properties that differ from those of aspherically symmetric ball. The latter symmetry requirement is tested bythe U.S.G.A. during the overall distance test and requires that a ballhave no statistically significant difference in carry distance greaterthan 4.0 yards, nor statistically significant in-flight-time differenceof more than 0.40 seconds regardless of which axis the ball is spinningaround when launched.

Golf balls are generally either wound or molded. Since molded golf ballsare cheaper to produce, many of the currently available golf balls aretwo-piece polymeric balls of uniform density cores. More recentdevelopments in golf ball design have resulted in golf balls that haveimproved moments of inertia by minimizing the density in the center ofthe ball and maximizing the density away from the center and near thecover or outer edge of the ball. This can result in a golf ball that hassimultaneous characteristics of low spin for maximum distance, as wellas maintaining “bite” for shorter shots approaching the putting green.These types of golf balls, however, have a number of shortcomings. Many,for instance, use fillers to increase the weight distribution of thegolf ball towards the cover of the ball, which tend to adversely affectthe ball's performance, such as with respect to rebound. Accordingly,there is a need for such golf balls that do not exhibit some or all ofthe shortcomings of these golf balls appearing in the art.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a golf ball having a hard sphere core orlayer with at least one feature for controlling or otherwise achieving adesired vibrational response exhibited by the ball, e.g., by controllingthe stiffness of the hard sphere. The stiffness of the sphere may becontrolled or tuned by including at least one groove or any otherindentation in the hard sphere core or layer. The groove or groovesserve to locally reduce the wall thickness of the sphere, therebyreducing the stiffness of the hollow metal sphere core by allowinglarger deformations under a given load without significantly reducingthe total mass of the sphere.

In one embodiment, the present invention includes a golf ball having acover formed of an ionomeric material or any other material that isresistant to damage from external articles of the type normallyencountered when playing golf. The cover has an outer surface, defininga dimpled pattern, and an inner surface, defining with the outer surfacea cover thickness. The ball also includes a hard sphere core or layer,such as one made from a metal, which has an outer surface and an innersurface, together defining a sphere thickness. In one embodiment, theouter surface of the sphere supports, and is surrounded by, the innersurface of the cover. In one embodiment, the outer sphere surfaceadvantageously includes at least one groove or other indentation forcontrolling the stiffness of the hard sphere. In another embodiment, theinner sphere surface advantageously includes at least one groove forcontrolling the stiffness of the sphere. In another embodiment, both theinner sphere surface and the outer sphere surface include at least onegroove for controlling the stiffness of the sphere.

In one aspect, the outer sphere surface individually, the inner spheresurface individually, or both the outer sphere surface and the innersphere surface, may also include a plurality of grooves where thegrooves may be in a regularly spaced pattern. The plurality of groovesmay include a plurality of regularly spaced horizontal grooves and aplurality of regularly spaced vertical grooves, where the plurality ofvertical grooves are essentially perpendicular to the plurality ofhorizontal grooves. The plurality of grooves may also include aplurality of angled grooves that intersect the plurality of regularlyspaced vertical grooves. Further, an intermediate layer or mantle may bedisposed between the hard sphere and the cover, the intermediate layercomprising a compressible and/or resilient material selected from thegroup consisting of natural rubber, synthetic polymer compounds, and acombination of the natural rubber and synthetic polymer compounds.

In another aspect, the present invention provides a hard sphere core foruse in a modern golf ball. The hard sphere core has an outer surface andan inner surface, together defining a core thickness, where the outercore surface individually, the inner core surface individually, or boththe outer core surface and the inner core surface have at least onegroove or any other type of indentation for controlling the stiffness ofthe sphere core. In one embodiment, the outer core surface individually,the inner core surface individually, or both the outer core surface andthe inner core surface may include a plurality of grooves forcontrolling the stiffness of the metal sphere core. The plurality ofgrooves may include a plurality of regularly spaced horizontal groovesand a plurality of regularly spaced vertical grooves, where theplurality of vertical grooves are essentially perpendicular to theplurality of horizontal grooves. The plurality of grooves may alsoinclude a plurality of angled grooves that intersect the plurality ofregularly spaced vertical grooves and the plurality of horizontalgrooves.

The present invention also provides a method of constructing a metalsphere core with controlled stiffness for use in a modern golf ball,where the metal sphere core has an outer surface and an inner surface,together defining a core thickness. In one embodiment, the methodincludes forming at least one groove or any other type of indentation inthe outer core surface for controlling the stiffness of the metal spherecore. In another embodiment, the method includes forming at least onegroove in the inner core surface for controlling the stiffness of themetal sphere core. In another embodiment, the method includes forming atleast one groove in the outer core surface and at least one groove inthe inner core surface, for controlling the stiffness of the metalsphere core.

The golf ball of the present invention has several advantages thatprovide a golf ball having a hollow hard sphere core in which thestiffness of the core may be controlled, while maintaining the highoverall moment of inertia for the golf ball. The golf ball includes acover layer and a hard sphere core that has an outer core surface and aninner core surface where the outer core surface has at least one, andpreferably a plurality of, regularly spaced horizontal grooves and aplurality of regularly spaced vertical grooves that serves to decreasethe stiffness of the hollow metal sphere core. The grooves are regularlyspaced in order to maintain a golf ball that will perform similarlyabout any axis of rotation, such that the golf ball will conform to thecurrent U.S.G.A. golf ball standard. This results in a hollow metalsphere core for a golf ball in which the stiffness may be controlled andthe effect on the high moment of inertia of the ball may be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a partial cross-sectional perspective view of a hollow coredgolf ball.

FIG. 2 is a partial cross-sectional perspective view of a golf ballaccording to one embodiment of the present invention.

FIG. 3 is a front plan view of a metal sphere core of a golf ballaccording to one embodiment of the present invention.

FIG. 4 is a cross sectional view of grooves disposed on a metal spherecore according of one embodiment of the present invention.

FIG. 5A and FIG. 5B are exemplary cross sectional depictions of grooveprofiles according to other embodiments of the present invention.

FIG. 6 is a perspective view depiction of groove lines on a metal spherecore according to another embodiment of the present invention.

FIG. 7 is a perspective view depiction of groove lines on a metal spherecore according to another embodiment of the present invention.

FIG. 8 is a perspective view depiction of groove lines on a metal spherecore according to another embodiment of the present invention.

FIG. 9 is a partial cross sectional view of a metal sphere coreaccording to another embodiment of the present invention.

FIG. 10 is a partial cross sectional view of a metal sphere coreaccording to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the invention are shown. Indeed, this invention may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Like numbers refer to like elementsthroughout.

In U.S. Pat. No. 6,004,225, which is hereby incorporated herein byreference, the present inventors provide a golf ball having a hollowsphere core and an outer layer surrounding the sphere. The hollow spherecore may be solid, e.g., non-perforated, perforated, or porous.According to one embodiment, the sphere has a specific gravity of 2.5 to20, a diameter range from 0.39 to 1.5 inches, and a thickness of 0.02 to0.25 inches. The cover material is an ionomer, urethane, balata, orsynthetic elastomer (e.g. SURLYN, produced by DuPont Company or IOTEKproduced by Exxon Mobil), or any other suitable material. The resultinggolf ball design maximizes the density toward the perimeter of the balland away from the center. Consequently, the moment of inertia isincreased and the spin is reduced, thereby, e.g., reducing hooks andslices.

Similarly, U.S. Pat. No. 6,705,957, which is also hereby incorporatedherein by reference, provides a three-layer ball with a hollow spherecore. A second layer is disposed between the sphere and the cover. Thesecond layer is a resilient material, preferably a synthetic polymercompound, such as polybutadiene, a natural rubber compound, or acombination thereof. The thickness of the second layer is about 0.05 to0.65 inches. This design also results in a golf ball that increases themoment of inertia and reduces spin, with the advantage of providing thedesigner with an additional degree of freedom to tailor the response ofthe ball to the impact of the golf club.

However in certain instances under high loads, a golf ball with a hardsphere layer or core, whether hollow or otherwise, can be excessivelystiff. In spite of the ball's reduced tendency to hook or slice, thisproduces performance characteristics, including sound, initial velocity,and distance, that may not be attractive to some golfers. In thisrespect, the present invention provides golf balls having a hard spherelayer or core with at least one feature associated with the hard sphereor with any other layer for controlling or otherwise achieving a desiredvibrational response to the impact of the golf club. A feature thatcontrols the vibrational response of the hard sphere or any other layergenerally modifies the manner in which the golf ball oscillates inresponse to an impact as compared to the response of the sphere or layerwithout the feature. This includes changes with respect to the initialdeflection or amplitude, frequency, wavelength, or the period of one ormore cycles of the waveform representing the vibrational response of theball, the number of cycles it takes to dampen out the vibration, etc. Inone embodiment, the first half of the sinusoidal waveform representingthe vibrational response after impact is tailored to occur in less thanor greater than 5 milliseconds, 7 milliseconds, 10 milliseconds, orgreater.

Referring to FIG. 1, a golf ball 10 having a cover 11 and a one-piecehollow core 12 is shown. During a high-speed collision with the face ofa clubhead (or the face of a rigid member), a golf ball undergoesdeformation such that the core of the ball deforms from a sphericalshape to an oblong shape. At the point of maximum deflection, the balland the clubhead travel together for a moment of time. After this point,the ball projects forward, pushing itself off of the face of the club.Based on the relative weight of the clubhead to that of the golf ball,the golf ball travels at a faster speed than the clubhead. The initialvelocity of the golf ball can be approximated with the followingequation: $v = {U \times \frac{1 + {COR}}{1 + ( {m/M} )}}$

where v is the velocity of the ball immediately after impact, U is thevelocity of the clubhead immediately before impact, m is the mass of theball, M is the mass of the clubhead, and COR is the coefficient ofrestitution of the ball.

With respect to the coefficient of restitution (‘COR’) of the golf ball,in general, if the COR in a given collision is high (i.e. near 1.0 or100%), then very little of the kinetic energy is lost during thecollision. However, if the COR in a given collision is low, then morekinetic energy is lost during the collision. The COR of a typicalpolymeric golf ball is around 70-85%, with the losses resulting frominternal friction between the polymeric molecules as the ball deformsfrom the spherical shape to an elongated sphere during maximumdeflection, and back to the spherical shape after impact.

The inventors have observed that in some instances, depending on thematerials used for construction, the COR of golf balls with hollow metalcores having a smooth surface or surfaces, such as that shown in FIG. 1,can be much less than 100%, in some cases ranging as low as 40%. Theinventors have also determined that a large fraction of the energylosses after impact are attributed at least in part to vibrations. Thatis, after impact the metal sphere can be seen as being displaced aboutan equilibrium position (e.g., from an essentially perfect sphere to anelongated sphere) and will oscillate about this equilibrium positionuntil internal and external frictional forces cause the vibration todecay. These vibrations are generally converted to thermal energy.

One parameter that plays a role in the vibrational response of a golfball having a hard sphere core or layer is the stiffness of the sphere.The stiffness may be attributed to either the properties of the materialused to construct the sphere, such as the hardness, modulus ofelasticity, toughness, etc., or properties associated with the shape andsize of the sphere, such as the moment of inertia, the section modulus,etc. In addition, the properties of the polymers or other materialssurrounding the sphere, as well as any materials within the sphere,affect the vibrational response. The ability to minimize or otherwisereduce vibrational losses will generally reduce the kinetic energy fromthe impact that is lost to heat, thereby increasing the COR of the ball.Another parameter that plays a role in the vibrational response of agolf ball is the ball's ability to dampen the vibrations caused byimpact. Damping may be attributed to the properties of the materialssurrounding or disposed within the hard sphere, such as the density,viscosity, modulus of elasticity, coefficients of friction, etc., of thematerials. The materials may be gases, pressurized or otherwise,liquids, gels, foams, solids, etc. Additionally, the state of thematerials is also a consideration, such as whether the materials areprestressed, etc. Any one of these parameters may be modified to tailorthe vibrational response of the golf ball.

The following equation describes the deflection response of a threepiece golf ball when struck during a high impact collision. It should benoted that although the equation describes the deflection of a threepiece ball, the analysis is equally valid for a two piece ball bysetting the portion relating to the mantle layer to zero.D=(d _(cover) +d _(mantle) +d _(core))

where D=the total deformation of the ball, d_(cover)=the deflection ofthe cover layer, d_(mantle)=the deflection of the mantle layer, andd_(core)=the deflection of the hollow sphere core, each of which is afunction of the force F applied to the ball. The deflections of thecover, mantle, and core are all non-linear functions of the appliedforce, thickness of the layer, configuration, and materials ofconstruction, respectively.

The hard hollow sphere core and a resilient mantle layer of a threepiece golf ball tends to deflect in a linear manner for small loads, andbecomes increasingly stiff and therefore non-linear as the loadincreases. A metal core is linear in its response to much higher loads.As a result, for shorter shots approaching the green, which are notstruck as hard as drives, the cover and the mantle provideproportionately more of the deformation of the ball than they do in adrive which exerts much higher forces to the ball. Therefore, a golfball can be thought of exhibiting a variable spring constant, with theconstant being primarily defined by the cover and mantle layers for lowenergy impacts and defined primarily by the hollow metal core for highenergy impacts.

Stiffness is directly related to the vibrational response of an object.The following equation for a simple harmonic oscillator relates thestiffness of a spring to various damping factors (including certainfrictional forces) and the resulting vibrational response:${\frac{\mathbb{d}^{2}x}{\mathbb{d}t^{2}} + {b\frac{\mathbb{d}x}{\mathbb{d}t}} + {\omega_{o}^{2}x}} = {A_{o}{\cos( {\omega\quad t} )}}$

where t is time, b is the damping constant, ω_(o) is the characteristicangular frequency (equal to 2πf_(O), where f is frequency in cycles persecond), A_(o) cos(ωt) (=A_(O) cos(2πft)) is the driving force with anamplitude of A_(O) and an angular frequency of ω, and x is the position.

Because the force exerted on a golf ball may be considered an impact orimpulse force, the initial conditions (t=0) are such that the right handside of the equation is zero. Focusing on the left hand side of theequation, the damping coefficient and characteristic angular frequencywill be important variables for design considerations in terms ofcontrolling the vibrational response of the ball. Since the dampingcoefficient will not determine the amount of energy coupled to thevibrational losses of the system, only the rate at which it isdissipated as heat, this shows that the characteristic frequency will bethe primary variable for designers to reduce energy losses associatedwith vibration. Characteristic frequency is a function of the stiffnessor spring constant of the sphere or ball, as well as the state of theprestress (compression or tension forces) on the sphere.

The inventors have determined that by increasing the amount ofdeflection that the hard sphere core or layer of the golf ball exhibitsfor a given impact, without decreasing the diameter of the core, e.g.,by decreasing the stiffness of the golf ball or the hard sphere, or thespring constant of the hard sphere, the COR of the ball may be increasedpreferably to greater than about 70%, or more preferably to greater thanabout 85% or about 90%, or even more preferably close to unity, with aminimal affect on the ball's high moment of inertia. Thus, increasingthe defection of the hard sphere core or layer of the golf ball wouldprovide additional design parameters and an ability to increase thetotal deflection of the ball without an associated increase in theball's tendency to hook or slice. This results in a golf ball that islegal for play and capable of drive distances essentially equivalent tothose of currently available high performance golf balls, but that alsomaintains a high moment of inertia, allowing less hooks and slicesduring play.

The present invention therefore generally provides golf balls having anouter cover with a dimpled pattern and a hard sphere layer or corehaving at least one feature associated with the hard sphere or with anyother layer for controlling the vibrational response of the hard sphereor the ball. The present invention may be applied toward two-piece golfballs in which instance the ball will consist of the cover with a hardsphere core, hollow or otherwise. The invention may also be appliedtoward other multi-piece designs using greater than two pieces, e.g.,three, four, five, etc. pieces, in which instance the hard sphere mayserve as an intermediate layer or as a sphere core, hollow or otherwise.The feature that controls the vibrational response of the hard sphere orof any other layer may be any feature that modifies the manner in whichthe golf ball responds to an impact as compared to the response of thesphere without the feature. The feature may be one that modifies, e.g.,reduces or increases, as the case may be, the stiffness, the amount ofdeflection for a given impact, the spring constant, the dampingcoefficient associated with the ball or sphere, or a combinationthereof. The modification may be accomplished by varying any parameterattributing to the stiffness, deflection, spring constant, or dampingcoefficient noted above.

Referring to FIG. 2, in one embodiment of, the present inventionprovides a golf ball 20 having a metal or other hard material spherecore or layer 27 surrounded by a cover layer 21, where the sphere core27 has at least one indentation or groove 23 or other means forcontrolling the vibrational response of the sphere, such as for reducingthe stiffness or spring constant, or increasing the deflection responseof the hard sphere core or layer 27 or increasing the dampingcoefficient against the hard sphere core or layer as compared to core orlayer without the feature. Hereinafter, the term “core” shall be used toinclude the term “layer”. The sphere may also be a one-piece design.Although the invention is described by way of example in relation tocertain types of materials, such as a metal sphere core, it isunderstood that the invention is equally applicable with other hardmaterials that do not appreciably deform under loads, such as plastics,e.g., polypropylene, ceramics, e.g., silicon carbide, composites, e.g.,carbon fiber and graphite, etc., and is thus not limited thereto.Additionally, although the invention is described by way of havingvertical or horizontal grooves, it is understood that a similar resultmay be achieved with other regularly patterned indentations, such aswith perforations, protrusions, or a combination thereof, that reducethe wall thickness of the hard sphere core at the desired locations toreduce the stiffness of the core thereby allowing larger deflections atimpact, e.g., elastic deformations, and is also not limited thereto.

The cover layer 21 has a cover outer surface 22 and a cover innersurface 24. The cover outer surface 22 and the cover inner surface 24together define a cover thickness 25, which is about 4 mm, but may beany thickness between about 1 mm and about 6 mm or between about 2 mmand about 5 mm. The cover 21 has a surface dimple pattern and ispreferably made of SURLYN, but may be also be made of an ionomer,urethane, balata, polybutadiene, or other synthetic elastomer, or anyother material suitable for a golf ball cover. The cover layer 21 alsoforms the golf ball diameter 26. The golf ball diameter is preferably42.67 mm (1.68 inches), but may be any diameter equal to, greater orless than 42.67 mm, preferably between about 40 mm and about 45 mm. Itshould be noted that the golf ball 20 of the present design may alsoinclude at least one intermediate layer (not shown) disposed between thecover layer 21 and the metal sphere core 27.

The golf ball 20 also includes a sphere core 27 having a diameter 31 andan outer core surface 28 and an inner core surface 29. Preferably, thediameter 31 of the metal sphere core 27 is about 31.75 mm (1.25 inches),but the diameter may be any diameter from about 10 mm (0.39 inches) toabout 38 mm (1.50 inches), or from about 25.4 mm (1.0 inches) to about35.6 mm (1.4 inches). The outer core surface 28 and the inner coresurface 29 together define a core thickness 30. The core thickness 30 ispreferably about 1.82 mm, however the core thickness 30 may be anythickness from about 0.5 mm to about 6.4 mm. The metal sphere core 27 ispreferably made of titanium or titanium alloy, but may also be made ofanother metal alloy including stainless steel, or an intermetallicmaterial such as aluminum. The metal sphere core 27 may also be made ofiron, carbon steel, nickel, molybdenum, aluminum, tungsten or alloys ofsteel, nickel, aluminum, molybdenum, or tungsten.

Advantageously, in one embodiment of the present invention, the outercore surface 28 of the metal sphere core 27 includes at least one groove23 for controlling or otherwise reducing the stiffness of the metalsphere core 27. The outer core surface 28 may include at least onehorizontal groove, and more preferably includes a plurality of regularlyor randomly spaced horizontal grooves 32. The outer core surface 28 mayalso include at least one vertical groove, and more preferably includesa plurality of regularly or randomly spaced vertical grooves 35. Thematerial displaced by the grooves may be replaced with a filler materialhaving a density greater than that of the cover layer or intermediatelayer, as the case may be. In the embodiment depicted in FIG. 3, theouter core surface 28 of the metal sphere core 27 includes a pluralityof regularly spaced horizontal grooves 32 and a plurality of regularlyspaced vertical grooves 35. The plurality of regularly spaced verticalgrooves 35 intersect and are substantially perpendicular to theplurality of regularly spaced horizontal grooves 33. In the depictedembodiment, the horizontal grooves 32 and the vertical grooves 35 arespaced at increments of about every ten degrees and may be manufacturedby any method suitable to form grooves in metal, including, but notlimited to laser cutting, mechanical stamping, casting, and chemicaletching.

Referring to FIG. 4, the horizontal grooves 32 and the vertical grooves35 define a groove width 33 and a groove depth 34. The groove width 33is preferably about 0.30 mm, or any width from about 1 nm to about 5 mm,and the groove depth 37 is preferably about 0.91 mm, but may be anydepth between 1 nm and 5 mm, depending on the thickness of the metalsphere core 27. The profile of the horizontal grooves 32 and verticalgrooves 35 is preferably u-shaped with right angles defining the maximumdepth, but may be any other profile or combinations of profiles suitablefor controlling the stiffness of the metal sphere core 27, including butnot limited to a profile having a u-shape with filleted angles definingthe maximum depth as shown in FIG. 5A, or a profile having a v-shape asshown in FIG. 5B.

It should be noted that the golf ball 20 of the present invention mayinclude other groove configurations or combinations of configurationsthat serve to control the vibrational response or stiffness of the metalsphere core 27. For example, at least one angled groove (not shown), andpreferably, a plurality of angled grooves may intersect the plurality ofvertical grooves 32. The groves or indentations may also be disposed ororiented in a random or an apparently random manner. In anotherembodiment, the plurality of horizontal grooves 32 and the plurality ofvertical grooves 35 may be configured along lines similar to latitudinaland longitudinal lines of a globe, as shown in FIG. 6, which shows alatitude and longitude lines oriented around a single axis. A pluralityof latitude and/or longitude lines may also be oriented around aplurality of axes, such as two axes, three axes, etc. The axes may beoriented at any angle from about 0 degrees to about 360 degrees fromeach other. In another embodiment, the plurality of horizontal grooves32 and the plurality of vertical grooves 35 may be configured alonghorizontal and vertical lines on each of the two or three axes of themetal sphere core 27, as shown in FIG. 7. In another embodiment, grooves23 may be configured along an icosahedron pattern as shown in FIG. 8.

In another embodiment, the inner core surface 29 of the metal spherecore 27 includes at least one groove 23 for controlling the stiffness ofthe metal sphere core 27. The inner core surface 29 may include at leastone horizontal groove, and more preferably includes a plurality ofregularly or randomly spaced horizontal grooves 32. The inner coresurface 29 may also include at least one vertical groove, and morepreferably includes a plurality of regularly or randomly spaced verticalgrooves 35. In the embodiment depicted in FIG. 9, the inner core surface29 includes a plurality of regularly or randomly spaced horizontalgrooves 32 and a plurality of regularly or randomly spaced verticalgrooves 35. In another embodiment, both the outer core surface 28 andthe inner core surface 29 may include at least one groove 23 forcontrolling the stiffness of the metal sphere core 27. In the embodimentdepicted in FIG. 10, both the inner core surface 29 and the outer coresurface 28 include a plurality of regularly spaced horizontal grooves 32and a plurality of regularly spaced vertical grooves 35. The orientationof the groves or indentation in the inner core surface may be anydescribed above with relation to the outer core surface. It shouldfurther be noted that one skilled in the art may conceive other possiblegroove configurations that may be included on the inner core surface 29,the outer core surface 28, or both the inner core surface 29 and theouter core surface 28, including, but not limited to the examples shownin FIG. 6, FIG. 7, and FIG. 8, and combinations thereof.

The golf ball 20 of the present invention has several advantages thatprovide a golf ball having a hollow metal or other hard material spherecore or layer in which the vibrational response stiffness may becontrolled, while maintaining a high overall moment of inertia for thegolf ball. The golf ball 20 includes a cover layer 21 and a hollow metalsphere core 27 that has an outer core surface 28 and an inner coresurface 29 where the outer core surface 28 has a plurality of regularlyspaced horizontal grooves 32 and a plurality of regularly spacedvertical grooves 35 that serve to decrease the stiffness of the metalsphere core 27. Additionally, the grooves are regularly spaced in orderto maintain a golf ball that will perform similarly about any axis ofrotation, such that the golf ball will conform with the current U.S.G.A.golf ball standard. This results in a hollow metal sphere core 27 for agolf ball 20 in which the stiffness may be controlled and the effect onthe high moment of inertia of the ball may be minimized.

The inventors have determined that a golf ball with a titanium metalcore having a 34.64 mm diameter, a 1.82 mm wall thickness, and onedegree thick grooves 0.91 mm deep spaced every ten degrees, and a 4 mmSurlyn cover, deformed 2.75 times more than a similar ball without thegrooves. Accordingly, the stiffness of the hard sphere may be reduced toas low as about 36% as compared with the sphere without the grooves. Itis understood that the depth, width, and number of grooves may be variedto achieve a desired stiffness. The reduced stiffness may also beachieved by one or more of the following: selecting materials and/orprocessing conditions for the mantle and/or cover to create aprestressed condition on the hard sphere, selecting materials withsuitable characteristics, altering the physical properties of thematerial used to construct the hard sphere, such as by annealing, hotworking, or cold working prior to or after hemisphere formation,preferentially etching material located within the grain boundaries ofthe metal sphere to remove material located with the grain boundaries ofthe bulk material, pressurizing the interior of the sphere, e.g., tocreate positive or negative pressure therein (to prestress the sphereeither positively or negatively), uniformly altering the gauge thicknessof the hard sphere, having the hard sphere consist of two or moreconcentric or layered hard spheres having preferred properties, or acombination thereof.

The material sets, polymer layers, and processing conditions may also betailored to achieve the desired vibrational response. The response andperformance of a finished golf ball is generally related to thecombination of materials used in construction. Each layer of the golfball will generally contribute to the overall response. That is, thefinal response will generally be the sum of the responses from theindividual layers and any interplay between the layers. The vibrationalresponse may therefore also be tailored by controlling the interplaybetween the layers of the golf ball of the present invention. Forexample, the cover layer or intermediate layer may be applied over thehard sphere core to prestress the sphere. This may be accomplished withrubber winding technology used with solid core golf balls, which windspolymers or rubber materials around the hard sphere to prestress thesphere. Other methods may be used to prestress the sphere, such as byusing oversized, undersized, or out of round metal hemispheres that areforced into the proper spherical form and size prior to welding.

Nano-materials may also be used as the feature to tailor the vibrationalresponse or other characteristics of the golf ball. Nanomaterials aregenerally those that exhibit characteristics based on controlling thecomposition of the material at a sub-micrometer level, to vary thestrength, ductility, hardness, formability, crack propagationresistance, etc., or a combination thereof. For example, materials, suchas metal, e.g., titanium, with controlled grain sizes may be used forthe hard sphere core with beneficial characteristics based on grainsize. For example, grain sizes may be increased to reduce stiffness orthe reverse. Composite materials may also be used to control thevibrational response or other characteristic of the golf ball. Forexample, by varying the amount of second phase dispersions within ametal matrix composite, the strength and stiffness of the base materialused for the sphere may be tailored. For example, alloying elements maybe introduced into the metal matrix to restrict dislocation movementthereby stiffening the material. Conversely, using essentially puremetals reduces the stiffness of the material. Additionally,nanomaterials may be used to control dispersoid-dislocationinteractions, e.g., Orowan bypassing, and Hall-Petch strengthening.Thus, nanosize materials, such as metallic, ceramic, or clay powders,carbon-nanotubes, etc., may be used as the second phase may not only tocarry a portion of the load on the hard sphere or any other layer, butmay also interact with the matrix material dislocations or grainboundaries to tailor the strength or stiffness of the sphere or anyother layer. For example, nano-ceramic or clay powders may be introducedinto a polymer mantle layer to achieve a desired vibrational responsefrom the ball.

The present invention generally provides golf balls that exhibit adesired vibrational response. Other hardware may similarly be tuned tothe vibrational response of the golf balls tuned in accordance with thepresent disclosure. For example, golf clubs, such as woods, irons,wedges, putters, etc., may be tuned to the golf ball to maximize thebeneficial characteristics of the golf balls.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1. A golf ball comprising: a cover layer having an outer surfacedefining a dimpled pattern and an inner surface defining with the outersurface a cover thickness; and a non-perforated hard sphere layer orcore disposed within the cover layer, the hard sphere having an outersurface and an inner surface together with the outer surface defining asphere thickness, wherein the hard sphere comprises at least one featurefor controlling a vibrational response of the hard sphere.
 2. A golfball according to claim 1, wherein the at least one feature forcontrolling the vibrational response of the hard sphere comprises atleast one indentation for controlling a stiffness of the hard sphere. 3.A golf ball according to claim 1, wherein the at least one indentationcomprises a groove.
 4. A golf ball according to claim 3, wherein atleast one of the outer sphere surface individually, the inner spheresurface individually, and both the outer sphere surface and the innersphere surface further comprises a plurality of grooves.
 5. A golf ballaccording to claim 4, wherein the plurality of grooves further comprisea plurality of regularly spaced horizontal grooves and a plurality ofregularly spaced vertical grooves, the plurality of vertical groovesbeing essentially perpendicular to the plurality of horizontal grooves.6. A golf ball according to claim 4, wherein the plurality of groovesfurther comprise a plurality of regularly spaced angled grooves thatintersect a plurality of regularly spaced vertical grooves and aplurality of horizontal grooves.
 7. A golf ball according to claim 3,wherein at least one of the outer sphere surface individually, the innersphere surface individually, and both the outer sphere surface and theinner sphere surface further comprises a plurality of regularly spacedgrooves.
 8. A golf ball according to claim 3, wherein the groove definesa groove width and a groove depth, wherein the groove width is betweenabout 1 nm to about 5 mm and the groove depth is between about 1 nm andabout 5 mm.
 9. A golf ball according to claim 1, further comprising aresilient intermediate layer disposed between the hard sphere and thecover.
 10. A golf ball according to claim 1, wherein the hard sphere isa metal sphere of a metal selected from the group consisting of titaniumand titanium alloys.
 11. A golf ball according to claim 1, wherein theat least one feature for controlling the vibrational response of thehard sphere comprises a plurality of indentations disposed randomly onat least one of the outer sphere surface and the inner sphere surface.12. A golf ball according to claim 1, wherein the thickness of the hardsphere core is between about 0.5 mm to about 6.4 mm.
 13. A golf ballaccording to claim 1, wherein the hard sphere is a hollow core.
 14. Agolf ball according to claim 13, wherein the hollow sphere comprises amaterial disposed within the hollow sphere to at least one of dampenimpact vibrations and prestress the hollow sphere.
 15. A golf ballaccording to claim 1, further comprising a resilient intermediate layerdisposed between the hard sphere and the cover to prestress the hardsphere.
 16. A golf ball comprising: a cover layer having an outersurface defining a dimpled pattern and an inner surface defining withthe outer surface a cover thickness; a hard sphere layer or coredisposed within the cover layer, the hard sphere having an outer surfaceand an inner surface together with the outer surface defining a spherethickness, wherein the hard sphere comprises at least one feature forcontrolling a vibrational response of the hard sphere; and a resilientintermediate layer disposed between the hard sphere and the cover.
 17. Agolf ball comprising: a cover layer having an outer surface defining adimpled pattern and an inner surface defining with the outer surface acover thickness; a metal sphere layer or core disposed within the coverlayer, the metal sphere having an outer surface and an inner surfacetogether with the outer surface defining a sphere thickness, wherein themetal sphere comprises at least one indentation for reducing a stiffnessof the metal sphere; and a resilient intermediate layer disposed betweenthe metal sphere and the cover.
 18. A metal sphere core for use in amodern golf ball, the metal sphere core having an outer surface and aninner surface, together defining a core thickness, wherein the outercore surface individually, the inner core surface individually, or boththe outer core surface and the inner core surface have at least onegrove for controlling the stiffness of the metal sphere core.
 19. Ametal sphere core according to claim 18, comprising a plurality ofgrooves, and wherein the outer core surface individually, the inner coresurface individually, or both the outer core surface and the inner coresurface comprise the plurality of grooves.
 20. A metal sphere coreaccording to claim 18, comprising a plurality of grooves, and whereinthe outer core surface individually, the inner core surfaceindividually, or both the outer core surface and the inner core surfacecomprise the plurality of regularly spaced grooves.
 21. A metal spherecore according to claim 18, comprising a plurality of grooves, andwherein the outer core surface individually, the inner core surfaceindividually, or both the outer core surface and the inner core surfaceincludes a plurality of regularly spaced angled grooves that intersectthe plurality of regularly spaced vertical grooves and the plurality ofhorizontal grooves.
 22. A metal sphere core according to claim 18,wherein the metal is selected from the group consisting of titanium andtitanium alloys.
 23. A method of constructing a metal sphere core withcontrolled stiffness for use in a modern golf ball, the metal spherecore having an outer surface and an inner surface defining with theouter surface a core thickness, the method comprising: forming at leastone indentation in the outer core surface individually, the inner coresurface individually, or both the outer core surface and the inner coresurface for controlling the stiffness of the metal sphere core.
 24. Amethod for constructing a golf ball comprising forming an intermediatelayer over a hard sphere layer or core, and forming a cover layer havingan outer surface defining a dimpled pattern over the intermediate layer,wherein at least one of the cover layer, intermediate layer, and spherelayer or core comprise at least one of a material selected to achieve adesired vibrational response from the ball and a property associatedwith a shape, size, and damping of the sphere or layer to achieve thedesired vibrational response from the ball.
 25. A method forconstructing a golf ball according to claim 24, wherein a plurality ofthe cover layer, intermediate layer, and sphere layer or core, comprisea material set tailored to achieve the desired vibrational response.